OB wants me to cut carbs

My most recent visit to the OB has left me very stressed. She wants me to cut carbs as much as I can so I don't gain as much weight as with baby #1. I'm 5'6 and 130lbs and last time I gained 55lbs and had a nearly 10lb baby. He got stuck and had shoulder dystocia and needed his collarbone to be fractured in order to come out. This time around, she said I do not automatically need a c-section but I should try very hard not to gain more than 20lbs to avoid the same type of birth trauma (lots of weight gain is linked to large babies). The thing is that I've never dieted in my life but still eat healthy. Also I don't feel like cutting carbs is a healthy thing durin pregnancy.
What is your opinion on dieting during pregnancy?